Plasma cell tumors in humans most commonly occur as multiple myeloma, an incurable form of cancer. Biochemical lesions involved in the development of these tumors have been difficult to characterize and the most common biological association with this disease is an apparent critical role of Interleukin-6. We have previously demonstrated a role for the Insulin-like growth factor receptor I (IGF-IR) signaling pathway in murine plasma cell tumor development. We have now extended these studies to human myeloma and characterized the biochemical elements and biological effects of signaling through this receptor. IGF-IR was found to be highly expressed in virtually all myeloma lines. Stimulation of myeloma lines with IGF-I lead to activation of two cellular signaling cascades. The first of these resulted in activation of mitogen activated protein kinases followed by cellular proliferation, and the second the activation of Akt kinase leading to inhibition of processes normally inducing cell death. The combined effects of stimulation of these two pathways suggest that IGF-I signaling may play a significant role in survival of myeloma cells. This possibility was tested in vivo where it was demonstrated that myeloma lines grew significantly faster in SCID mice treated with IGF-I as compared to untreated controls. Additional studies relating to the importance of this pathway revealed defects in 2/8 lines in the tumor suppressor gene PTEN which participates in regulation of the apoptotic arm of IGF signaling. Mutation of this gene in one line lead to marked inhibition of cell death and re-introduction of a normal PTEN gene not only restored normal function, but prevented tumor growth in vivo . In an attempt to identify lesions contributing to either initiation or progression of multiple myeloma, we have initiated expression cloning studies to identify candidate genes. Expression cDNA libraries have been constructed from myeloma lines and transfected initially into NIH 3T3 cells. Transformed colonies have been isolated and rescued genes are currently being analyzed. The first of these to be characterized is a cellular Ras gene which contains an uncommon mutation at position 117. Additional genes from these libraries are under study. The libraries are also being introduced into IL-6 dependent B9 cells and IL-3 dependent 32D cells in an attempt to identify expressed genes which will abrogate the requirement for these cytokines. Protocols are currently being established to obtain materials from early diagnosis myeloma patients in order to construct similar expression libraries and search for biochemical lesions in primary disease. This project was formerly Z01 BC 05553-28 LG